I have been a member of the Investment plan for many years.
The basics are you have to pay $10 to set it up.
You must already own ten shares, or make an initial invstment of at least $1,000, or set up automatic payments of at least $100 per month.
Once it is set up they charge 1¢ per share purchased or sold. In addition they charge $1 per purchase transaction from automatic payment or $5 per purchase transaction by check.